Explosive compositions may be divided into two categories: molecular or homogeneous explosives, wherein the molecule of the compound contains chemical moieties which confer explosive properties, and composite or heterogeneous explosives wherein mixtures of fuels and oxidizers can be made to be explosive.
Composite explosives are made by mixing oxidizing salts, usually perchlorates or nitrates, with appropriate amounts of organic or metallic fuels. Many useful explosives are thus made, and it has been found that such mixtures are improved in utility and performance by formulating the mixtures as slurries or emulsions, which improves the intimacy of contact between the fuel and oxidizer. Further, such compositions are pumpable, which greatly facilitates their manufacture and placement for use.
Another type of composite explosive is made by mixing two or more molecular explosives. Typical of these are melt-cast formulations which are widely used as fills for military explosive ordinance. A commonly used explosive mixture is made by melting trinitrotoluene (TNT), which melts at a relatively low temperature, and then introducing into the liquid TNT matrix a large fraction of a granular solid explosive such as cyclotrimethylenetrinitramine (RDX) of higher melting temperature which is dispersed and suspended as a particulate solid in the TNT matrix. This mixture can be poured at temperatures above the TNT melting point, and upon cooling the mixture becomes hard.
Because of the high cost of TNT, efforts have been and are being made to employ eutectic mixtures of inorganic oxidizers (principally ammonium nitrate) and explosive compounds such as ethylenediaminedinitrate as a replacement for TNT.
Both the hard melt-cast composite formulations and the soft emulsion or slurry composite formulations are successful, but each suffers from certain disadvantages.
Mixing of molecular explosives is usually accomplished in melt kettles where large quantities of explosives are present in one mass and large distances must separate accumulated quantities of explosives. Of concern are the hazards associated with long dwell times at elevated temperatures because of the increased hazards at higher temperatures. Also troublesome is the shrinkage of these mixtures upon cooling and solidification along with accompanying density gradients, all of which must be accomodated for proper ordnance design.
The direction of development of emulsions and slurries has been toward soft or pumpable explosives for commercial blasting operations. Recent developments in such explosive formulations have been water-in-fuel emulsions, having soft or semi-soft consistencies. Patents for such emulsions teach stabilization techniques and fuel-phase continuity.
A further development is disclosed in two U.S. Pat. Nos. 4,248,644 and 4,391,659 which teach melt-in-fuel emulsion technology. As taught by these patents, either aqueous salt solutions or essentially anhydrous molten salts can be emulsified with an immiscible hydrocarbon fuel. The hydrocarbon fuel becomes the continuous phase. The discontinuous droplets of oxidizer are very small, and an extremely intimate mixture of fuel and oxidizer is thus obtained. In such oil-continuous emulsions, coalescence and crystallization of the discontinuous droplets of oxidizer may be prevented by making the droplets of oxidizer sufficiently small, and the surface tension such that nucleation may be inhibited; supersaturation or supercooling is achieved, and the emulsion, even though made with molten oxidizer, is formulated to be grease-like or extrudable at ambient temperature.
The stabilization of the oil-continuous emulsified state has been a principal objective of recent developments. A soft consistency is desirable for many applications in commercial blasting, and emulsions provide extremely intimate mixtures in a meta-stable state, giving them distinct advantages in explosive sensitivity. Stabilization of the emulsion has been considered desirable since crystallization of the oxidizer salts is accompanied by desensitization of the explosive. In non-aqueous emulsions, sensitivity loss is usually more significant than in aqueous emulsions. Another reason for stabilization of oil-continuous emulsions is to provide and maintain excellent water resistance, as water is effectively kept away from soluble salts by an oil continuum.
It has not been apparent heretofore that acceptable, indeed excellent, explosive performance is attainable by deliberate destabilization of an emulsion. It has also not been apparent that excellent water resistance is likewise attainable. In fact, anhydrous, oil-continuous emulsion destabilization has not been disclosed, and thus there is no directly pertinent prior art to this invention.
It is the principal objective of this invention to obtain solid, microcrystalline compositions employing essentially anhydrous inorganic oxidizers and hydrocarbon fuels wherein the intimacy of ingredients in the final product is sufficient to obtain excellent explosive and physical characteristics.
It is another objective to formulate the compositions in a manner which will permit continuous processing, cooling, optional admixing of additives, and loading or packaging before solidification.
Still another objective is to obtain, by extending the range of useable ingredients beyond that which has been applicable to stabilized emulsions or melt-cast explosives, explosive characteristics superior to those which have hitherto been obtained.
A further objective is to achieve water resistance in the explosive compositions.